Additional Information

Water supply forecasts take into consideration present hydrometeorological
conditions and use average basin temperatures and precipitation for the
forecast period. As the forecast season progresses, a greater portion of the
future hydrologic and climatic uncertainty becomes known and monthly forecasts
become more accurate.

Volume forecasts represent adjusted flows; that is, observed flows with
upstream water use taken into account. Adjusted flows will closely approximate
natural or unimpaired flows. However, not all upstream diversions or
impoundments are measured or quantifiable. For specific adjustments used with
each forecast point, consult the Guide to Water Supply Forecasting.

The Water Supply Outlook is issued monthly January through April by the
Colorado Basin River Forecast Center, National Weather Service. It represents
a coordinated effort between the National Weather Service, Natural Resources
Conservation Service, Bureau of Reclamation, Salt River Project, U.S.
Geological Survey and local water district managers.

DEFINITIONS:

Acre-Foot:

The volume equal to one acre covered one foot deep (43,560 cubic feet).

Average:

The arithmetic mean. The sum of the values divided by the number of values.

Categories:

Much above Average Above Average Near Average Below Average Much below Average
Greater than 130% 111 -130% 90-110% 70-89% Less than 70%

Forecast Period:

Variable. Current month through May 31.

Median:

The middle value. One half of the observed values are higher and half of the
values are lower than this.

Most Probable Forecast:

Given the current hydrometeorological conditions to date, this is the best
estimate of what the runoff volume will be this season.

Reasonable Maximum Forecast:

Given the current hydrometeorological conditions, the seasonal runoff that has
a ten percent (10%) chance of being exceeded.

Reasonable Minimum Forecast:

Given the current hydrometeorological conditions, the seasonal runoff that has
a ninety percent (90%) chance of being exceeded.

Water Year:

The period from October 1 through September 30.

NOTE: Data used in this report are provisional and are subject to revision.